1. Technical Field
The present invention relates to a light guide, a light guiding device and an image reading apparatus, and more particularly to an image reading apparatus configured to optically read an image of a document, and a light guide and a light guiding device preferably for use in the image reading apparatus.
2. Description of Related Art
In an image reading apparatus called a scanner, generally, either a reading system including an illumination unit extending in a main-scanning direction or an object, such as a document, to be subjected to image reading is moved in a sub-scanning direction, so that the image of the document can be read two-dimensionally. As a light source for the image reading, a fluorescent lamp is conventionally used. In recent years, however, replacement of the fluorescent lamp with an LED is accelerated. Unlike a fluorescent lamp, an LED is a point light source. Therefore, when an LED is used as a light source in an image reading apparatus, normally, a light guide as disclosed by Japanese Patent Laid-Open Publication No. 2012-248489 is also used so as to achieve linear light distribution needed for scanning. Such a light guide reflects light input from the LED on a prism provided therein so as to illuminate an object to be read. With respect to such a light guide, an improvement in the ratio of the quantity of light emitted from the light guide for illumination of the object to be read to the quantity of light input to the light guide (i.e., the light use efficiency) with maintenance of good light distribution is demanded.